Re: [dpdk-dev] [PATCH v3] alarms: Change alarm cancel function to be thread-safe

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, Oct 01, 2014 at 03:20:22PM +0100, Pawel Wodkowski wrote:
> v3:
> Set rte_errno inside rte_alarm_cancel() to inform caller about canceling result.
> 	
> v2:    
> Eliminate a race between rte_alarm_set() used in context of executing callback
> function and other threads that use rte_alarm_cancel().
> 
> Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
> ---
>  lib/librte_eal/common/include/rte_alarm.h |   12 ++++-
>  lib/librte_eal/linuxapp/eal/eal_alarm.c   |   83 ++++++++++++++++++++---------
>  2 files changed, 68 insertions(+), 27 deletions(-)
> 
> diff --git a/lib/librte_eal/common/include/rte_alarm.h b/lib/librte_eal/common/include/rte_alarm.h
> index d451522..d5d4e9d 100644
> --- a/lib/librte_eal/common/include/rte_alarm.h
> +++ b/lib/librte_eal/common/include/rte_alarm.h
> @@ -76,7 +76,8 @@ typedef void (*rte_eal_alarm_callback)(void *arg);
>  int rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb, void *cb_arg);
>  
>  /**
> - * Function to cancel an alarm callback which has been registered before.
> + * Function to cancel an alarm callback which has been registered before. If
> + * used outside alarm callback it wait for all callbacks to finish execution.
>   *
>   * @param cb_fn
>   *  alarm callback
> @@ -86,7 +87,14 @@ int rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb, void *cb_arg);
>   *  can be used here.
>   *
>   * @return
> - *  - The number of callbacks removed
> + *    - value greater than 0 and rte_errno not changed - returned value is
> + *      the number of canceled alarm callback functions
> + *    - value greater or equal 0 and rte_errno set to EINPROGRESS, at least one
> + *      alarm could not be canceled because cancelation was requested from alarm
> + *      callback context. Returned value is the number of succesfuly canceled
> + *      alarm callbacks
> + *    -  0 and rte_errno set to ENOENT - no alarm found
> + *    - -1 and rte_errno set to EINVAL - invalid parameter (NULL callback)
>   */
>  int rte_eal_alarm_cancel(rte_eal_alarm_callback cb_fn, void *cb_arg);
>  
> diff --git a/lib/librte_eal/linuxapp/eal/eal_alarm.c b/lib/librte_eal/linuxapp/eal/eal_alarm.c
> index 480f0cb..4801650 100644
> --- a/lib/librte_eal/linuxapp/eal/eal_alarm.c
> +++ b/lib/librte_eal/linuxapp/eal/eal_alarm.c
> @@ -69,7 +69,8 @@ struct alarm_entry {
>  	struct timeval time;
>  	rte_eal_alarm_callback cb_fn;
>  	void *cb_arg;
> -	volatile int executing;
> +	volatile uint8_t executing;
> +	volatile pthread_t executing_id;
>  };
>  
>  static LIST_HEAD(alarm_list, alarm_entry) alarm_list = LIST_HEAD_INITIALIZER();
> @@ -108,11 +109,13 @@ eal_alarm_callback(struct rte_intr_handle *hdl __rte_unused,
>  			(ap->time.tv_sec < now.tv_sec || (ap->time.tv_sec == now.tv_sec &&
>  						ap->time.tv_usec <= now.tv_usec))){
>  		ap->executing = 1;
> +		ap->executing_id = pthread_self();
>  		rte_spinlock_unlock(&alarm_list_lk);
>  
>  		ap->cb_fn(ap->cb_arg);
>  
>  		rte_spinlock_lock(&alarm_list_lk);
> +
>  		LIST_REMOVE(ap, next);
>  		rte_free(ap);
>  	}
> @@ -145,7 +148,7 @@ rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb_fn, void *cb_arg)
>  	if (us < 1 || us > (UINT64_MAX - US_PER_S) || cb_fn == NULL)
>  		return -EINVAL;
>  
> -	new_alarm = rte_malloc(NULL, sizeof(*new_alarm), 0);
> +	new_alarm = rte_zmalloc(NULL, sizeof(*new_alarm), 0);
>  	if (new_alarm == NULL)
>  		return -ENOMEM;
>  
> @@ -156,7 +159,6 @@ rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb_fn, void *cb_arg)
>  	new_alarm->cb_arg = cb_arg;
>  	new_alarm->time.tv_usec = (now.tv_usec + us) % US_PER_S;
>  	new_alarm->time.tv_sec = now.tv_sec + ((now.tv_usec + us) / US_PER_S);
> -	new_alarm->executing = 0;
>  
>  	rte_spinlock_lock(&alarm_list_lk);
>  	if (!handler_registered) {
> @@ -202,34 +204,65 @@ rte_eal_alarm_cancel(rte_eal_alarm_callback cb_fn, void *cb_arg)
>  {
>  	struct alarm_entry *ap, *ap_prev;
>  	int count = 0;
> +	int err = 0;
> +	int executing;
>  
> -	if (!cb_fn)
> +	if (!cb_fn) {
> +		rte_errno = EINVAL;
>  		return -1;
> -
> -	rte_spinlock_lock(&alarm_list_lk);
> -	/* remove any matches at the start of the list */
> -	while ((ap = LIST_FIRST(&alarm_list)) != NULL &&
> -			cb_fn == ap->cb_fn && ap->executing == 0 &&
> -			(cb_arg == (void *)-1 || cb_arg == ap->cb_arg)) {
> -		LIST_REMOVE(ap, next);
> -		rte_free(ap);
> -		count++;
>  	}
> -	ap_prev = ap;
>  
> -	/* now go through list, removing entries not at start */
> -	LIST_FOREACH(ap, &alarm_list, next) {
> -		/* this won't be true first time through */
> -		if (cb_fn == ap->cb_fn &&  ap->executing == 0 &&
> +	do {
> +		executing = 0;
> +		rte_spinlock_lock(&alarm_list_lk);
> +		/* remove any matches at the start of the list */
> +		while ((ap = LIST_FIRST(&alarm_list)) != NULL &&
> +				cb_fn == ap->cb_fn &&
>  				(cb_arg == (void *)-1 || cb_arg == ap->cb_arg)) {
> -			LIST_REMOVE(ap,next);
> -			rte_free(ap);
> -			count++;
> -			ap = ap_prev;
> +
> +			if (ap->executing == 0) {
> +				LIST_REMOVE(ap, next);
> +				rte_free(ap);
> +				count++;
> +			} else {
> +				/* If calling from other context, mark that alarm is executing
> +				 * so loop can spin till it finish. Otherwise we are trying to
> +				 * cancel our self - mark it by EINPROGRESS */
> +				if (pthread_equal(ap->executing_id, pthread_self()) == 0)
> +					executing++;
> +				else
> +					err = EINPROGRESS;
> +
> +				break;
> +			}
>  		}
>  		ap_prev = ap;
> -	}
> -	rte_spinlock_unlock(&alarm_list_lk);
> +
> +		/* now go through list, removing entries not at start */
> +		LIST_FOREACH(ap, &alarm_list, next) {
> +			/* this won't be true first time through */
> +			if (cb_fn == ap->cb_fn &&
> +					(cb_arg == (void *)-1 || cb_arg == ap->cb_arg)) {
> +
> +				if (ap->executing == 0) {
> +					LIST_REMOVE(ap,next);
> +					rte_free(ap);
> +					count++;
> +					ap = ap_prev;
> +				} else if (pthread_equal(ap->executing_id, pthread_self()) == 0)
> +					executing++;
> +				else
> +					err = EINPROGRESS;
> +			}
> +			ap_prev = ap;
> +		}
> +		rte_spinlock_unlock(&alarm_list_lk);
> +	} while (executing != 0);
> +
> +	if (count == 0 && err == 0)
> +		rte_errno = ENOENT;
> +	else if (err)
> +		rte_errno = err;
> +
>  	return count;
>  }
> -
> -- 
> 1.7.9.5
> 
> 
Much better, thanks!
Acked-by: Neil Horman <nhorman@tuxdriver.com>